The present invention relates to a multilayer insulation composite and, more particularly, a multilayer insulation composite containing silica aerogel granules.
A common type of insulation used for cryogenic applications is multilayer insulation. Multilayer insulations typically consist of alternating layers of highly reflecting material, such as aluminum foil or aluminized mylar, and a low-conductivity spacer material or insulator, such as fiberglass mat or paper, glass fabric, or nylon net. Between twenty and forty such layers are commonly used for cryogenic applications including, for example, laboratory dewars, piping, on-site storage vessels, and tank trucks. In addition, multilayer insulations are advantageously kept under a high vacuum, thereby further enhancing the insulating properties of the multilayer insulations. Multilayer insulations have a very low thermal conductivity due to the fact that all modes of heat transferxe2x80x94conductive, convective, and radiativexe2x80x94are minimized. The multiple layers of reflecting material have a low emissivity and, thereby, inhibit radiative heat transfer. Convective heat transfer is inhibited by lowering the pressure (i.e., creating a vacuum) between the insulation layers. Finally, the presence of spacer material inhibits conductive heat transfer through thermal short-circuits that might otherwise exist between the layers of reflecting material.
Current multilayer insulations, however, are disadvantageous due to the need for complex vacuum pumping equipment to maintain the insulation in a highly evacuated environment. Typical multilayer insulations require vacuum levels on the order of 10xe2x88x927 to 10xe2x88x925 kPa (10xe2x88x926 to 10xe2x88x924 torr) to achieve suitable thermal performance. To sustain this low vacuum level, time consuming and expensive pumping and heating cycles are required as well as the addition of hydrogen and water getters/adsorbers. For some cryogenic applications, it would be advantageous to obtain similar thermal performance from the multilayer insulation at higher pressures in order to reduce costs associated with obtaining a vacuum.
Therefore, it is an object of this invention to provide a multilayer insulation composite which exhibit satisfactory thermal performance in cryogenic applications under higher pressures. It is another object of this invention to provide a multilayer insulation composite which exhibits improved thermal performance in cryogenic applications at low vacuum levels. These and other objects and advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.
The present invention is an insulating composite comprising (a) a first thermally reflective layer having a reflective surface and an opposing surface and (b) silica aerogel granules. The present invention further includes an insulating element in which the insulating composite is disposed within an air-impermeable container.